1. Field of the Invention
The present invention is directed to the arrangement of ink ducts in a printer head for an ink-jet printer unit, wherein the ducts proceed through the printer head in a manner approaching one another in the direction toward the printing location.
2. The Prior Art
An electrically operated ink-jet mosaic printing device in which ink droplets are sprayed from several jets against a recording medium to form a grid shaped character by means of piezoelectric drive elements contained in each of the ink ducts is disclosed in U.S. Pat. No. 4,158,847 (corresponding to German OS No. 2543451). There, the ink ducts extend through the printer head in the form of cylindrical tubes of uniform cross-section between a printing liquid reservoir on one side of the printer head and a printing location on the other side of the printer head where the ink ducts terminate in outlet orifices. A jet plate may also be provided at the printing location of the printer head to provide narrow jet bores which serve as the corresponding outlet orifices for the ink ducts. The piezoelectrical drive elements are individually activated to generate a compression wave in the interior of the ink duct and bring about the ejection of a defined ink droplet. The number of ink ducts and their spacial arrangement at the printing location depends upon the size of a desired printing grid and upon the desired resolution of the ink droplets on the recording medium within the grid. U.S. Pat. No. 4,158,847 concerns the arrangement of ink ducts extending diagonally away from the printing location in a manner free of kinks. This arrangement makes possible, on the one side, to bring spacially close together the downstream ends of the ink ducts in the vicinity of the printing location and, on the other side of the printer head, to provide greater spacing apart of the ink ducts from one another to mount the drive elements for the individual ink ducts with the required control lines. Accordingly, a simple structure of the printing head is attained and its size is reduced to a handy mass.
A drawback associated with the ink duct arrangement described in U.S. Pat. No. 4,158,847 is that the printing quality attained thereby does not always correspond to the desired requirements as a result of the funnelling together of the ink ducts at the printing location or at the jet plate. This results because the discharge orifices of the ink passages cannot be brought as close together to one another as may be desired. Decreasing the space between the downstream ends of the ink ducts at the printing location by the use of thinner ink ducts is not practical, since this approach interferes with flow and technological manufacturing limits. The use of very narrow, long ink ducts causes high flow losses in the ink passages, which leads to the need for increased voltages for operation of the drive elements.
The present invention overcomes this drawback by creating an arrangement which makes possible a narrower separation of the ink ducts in the vicinity of the printing location and thus affords higher ink jet printing resolution, without incurring high flow losses in the ink ducts.